1. Field of the Invention
The present invention relates to a multifunctional switching, apparatus assigned to a plurality of operating functions, and more particularly to a vehicle operating system using this multifunctional switching apparatus.
2. Prior Art
This type of multifunctional switching apparatus is, for example, incorporated in a vehicle operating system shown in FIGS. 12 and 13.
FIG. 12 is a plan view showing a conventional steering wheel equipped with a steering switch serving as a multifunctional switching operating apparatus. In FIG. 12, reference numeral 2 represents a steering switch constituted by a combination of push switch sections 3 and a seesaw switch section 4 or as a united assembly with a single operating switch. The steering switch 2 is disposed on a steering wheel 1 at an appropriate portion. Thus, the steering switch 2 is easy to operate and good-looking.
FIG. 13 is a circuit block diagram showing details of a conventional steering switch circuit. Resistors 5 and switches 6 are combined. When one switch is closed, a resistance value corresponding to the closed switch is produced for this switch. The output signal thus produced is sent from the steering switch 2 to the switch unit 8 via a connecting section 7. The switch unit 8 is disposed under the steering switch 2. The signal, after entered in the switch unit 8, is divided into a voltage value according to a predetermined ratio determined by a given resistor 9. The closed switch is thus identified according to this voltage value. A control signal, responsive to the closed switch, is sent to a corresponding vehicle device 10. In this manner, the designated vehicle device is remote controlled.
However, according to the above-described conventional multifunctional switching apparatus for the electrically controlled devices mounted in an automotive vehicle, the fundamental circuit arrangement is such that each switch exclusively controls the resistance value of an associated resistor. Thus, one switch is basically dedicated to only one function. In other words, the number of switches to be provided is basically identical with the number of functions required.
To satisfy various needs for the recent trend toward multifunction, a key is to solve a problem of space utility in a layout of all the necessary switches in a limited space. Of course, reducing the size of each operating section is important. If each operating section shares a larger space, a total operational area necessary for an operator to manipulate will become significantly larger. A finger shift amount becomes large with increasing size of the total operational area. This makes the operation difficult.
Such a difficulty is not resolved by an operator's learning of positions of respective operational switches. Identifying each switch by a finger touch was not feasible. Thus, a visual observation by an operator was necessary to confirm each switch when operated.
However, this forces the driver to change his/her eyes' direction from the forward direction to the switch. Enforcing the driver to look at each operating section for manipulating the switch is not desirable, in view of driving safety during a traveling of a vehicle.
Furthermore, the above-described method of combining resistors with switches is realized at a relatively low cost. However, when this method is applied to realize a multifunctional system, a reference voltage needs to be divided finely into smaller fractions to allocate it to numerous switching functions. A problem in dividing the reference voltage so finely is that a voltage range allocated to each function becomes very small. This possibly increases the probability of causing a malfunction of the controlled device by the influence of incoming noise or contact resistance of a connector.
Furthermore, when two or more switches are simultaneously closed, a composite resistance value of respective resistance values of these operated switches is produced. The resultant resistant value thus produced momentarily is different from each resistant value of the operated switches. It possibly results in an erroneous judgement in a vehicle control circuit, leading to a malfunction of the controlled device.